The present invention concerns a novel photometer and method for determining the absorbance ratio, in a sample, of two lights of different wavelengths. The illustrative embodiment of the invention is directed to a spectrophotometer for determining the presence of hemoglobin in a fluid and is a modification of the photometric apparatus and method disclosed in U.S. application Ser. No. 127,732, filed Mar. 6, 1980, now U.S. Pat. No. 4,305,659.
In various applications it is necessary to detect low levels of the various hema complexes, and most particularly oxyhemoglobin and free hemoglobin in a certain fluid. For example, in systems in which plasma is collected, it is often desirable to detect the presence of low levels of hemoglobin in the collected plasma.
In one prior art type of system for detecting hemoglobin in a fluid, the loss of light traveling through the sample is detected. To this end, the operator starts the fluid flow and the output is initially set to zero. Any change in this zero output level is detected and is considered a measure of the increased level of hemolysis. One problem in connection with this prior art device is the fact that a change in turbidity might be detected as an increased level of hemolysis. Another problem is that this prior art system requires an initial zeroing procedure which must be handled properly by an operator. A further problem with respect to this prior art system is that it is subject to changes in ambient light levels.
In copending application Ser. No. 127,732, filed Mar. 6, 1980, now U.S. Pat. No. 4,305,659, a hemolysis detector is disclosed which determines the red/green absorbance ratio of the sample. In this manner, the presence of even small traces of hemoglobin can be detected in a fluid, such as plasma. In the copending application, intensity leveling of the two light sources is required. The present invention obviates the need for such intensity leveling by utilizing a direct division of the light outputs. Further, by utilizing the present invention the output of the system may be in the form of a digital word, thereby enabling efficient and inexpensive display of the result in a digital form. Another advantage of the present invention is that the absolute magnitude of the signals produced by the light sources is relatively unimportant, so long as the relative ratio of the light source outputs tends to remain constant.
It is, therefore, an object of the present invention to provide an apparatus and method for determining the absorbance, in a sample, of two different wavelength lights.
Another object of the present invention is to provide a hemolysis detector which operates to detect hemoglobin in a fluid by determining the red/green absorbance ratio of the fluid.
Another object of the present invention is to provide a system for determining the color of a sample by using known absorbance characteristics and passing two colors through the sample and then determining the ratio of absorbance of the two colors.
A still further object of the present invention is to provide apparatus and a method for determining the color absorbance ratio of a fluid with the apparatus and method being blind to ambient light level changes.
A further object of the present invention is to provide an apparatus for determining the color absorbance ratio of a sample, with the apparatus being relatively simple in construction and easy to manufacture.
Another object of the present invention is to provide a system for determining the color absorbance ratio of a sample, without requiring intensity leveling of the light sources.
A further object of the present invention is to provide a system for determining the color absorbance ratio of a sample, and for enabling the display of the results in a digital form without requiring complex digital circuitry.
Other objects and advantages of the invention will become apparent as the description proceeds.